Primary care

What is a blood draw ?

During a blood draw, a health care professional draws blood from the vascular system for testing.

Blood is always taken under sterile (aseptic) conditions to minimise the risk of infection at the puncture site.

When do you do a blood draw?

In addition to blood donations, blood is primarily taken to obtain information. The blood count allows doctors to draw conclusions about diseases or deficiencies based on the composition of the blood. Blood consists of red blood cells (erythrocytes), white blood cells (granulocytes), platelets (thrombocytes), clotting agents and blood serum with proteins, electrolytes, nutrients and hormones. For example, an increase in the so-called C-reactive protein indicates an infection. In addition, an arterial blood sample can be taken as part of the gas analysis.

What is the procedure for a blood sample?

The most common type is venous blood sampling from the crook of the elbow. The cuff, the so-called tourniquet, is placed on the arm and tightened so that on the one hand blood can accumulate in the veins and on the other hand you can still feel the arterial pulse. 

The doctor feels the best puncture site and disinfects it thoroughly. Now the vein is punctured with a needle or with the so-called butterfly system, where the needle is also passed through two wings. The puncture through the skin may cause slight, short-lived pain. Blood collection tubes are attached to the tip of the needle and a vacuum is created by means of a plunger, which speeds up the blood collection.

When the tube is sufficiently filled, it is removed from the needle, the plunger is bent and the tube is tilted a few times. This causes the blood to combine with anticoagulants or other reagents already in the tubes and not clot. The most common is EDTA blood, in which the blood components remain unbound due to the ethylenediaminetetraacetate (EDTA) contained in the tube. Only in this way can the cells be examined in the laboratory.

Finally, the doctor opens the tourniquet, pulls out the needle and presses on the puncture site with a compress to prevent bruising. A plaster protects against infection.

Do I have to be sober for a blood sample? 

It is important that you come to the blood collection on an empty stomach so that your blood values are affected as little as possible. What does fasting for a blood sample mean? Basically, it means that you should not eat anything eight to twelve hours beforehand. This makes it easier to compare your blood values, as food mainly affects blood sugar and blood fat levels. The enzyme balance also changes as soon as the organs start digesting.